Brief Answer:
Dry eye or blepharitis

Detailed Answer:

Hello,

The sensation of "little rocks" or sand or gritty eyelids is causes by lack of fluids between the eye and the eyelid, causing friction. The reasons for this can be many, such as infection of the eyelid (blepharitis), dry eye syndrome, use of certain medications, etc. Sometimes, sleeping with an incompletely shut eyelid, or being next to an air vent or ceiling fan for too long can cause dryness. Blockage of a tear canal can also be a cause.

I recommend you use over the counter artificial tears for one or two days and see id if it gets better. If it doesn't I strongly recommend you see an ophthalmologist for a closer inspection as this may be a condition that needs proper treatment.

I hope this answers your question. Let me know if I can assist you further.
Take care

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